In this specification, abbreviated names of halogenated hydrocarbon compounds are described in brackets after the compound names, and in this specification, the abbreviated names are employed instead of the compound names as the case requires.
Heretofore, as a working fluid for a heat cycle system such as a refrigerant for a refrigerator, a refrigerant for an air-conditioning apparatus, a working fluid for power generation system (such as exhaust heat recovery power generation), a working fluid for a latent heat transport apparatus (such as a heat pipe) or a secondary cooling fluid, a chlorofluorocarbon (CFC) such as chlorotrifluoromethane or dichlorodifluoromethane or a hydrochlorofluorocarbon (HCFC) such as chlorodifluoromethane has been used. However, influences of CFCs and HCFCs over the ozone layer in the stratosphere have been pointed out, and their use is regulated at present.
Under the above conditions, as a working fluid for a heat cycle system, a hydrofluorocarbon (HFC) which has less influence over the ozone layer, such as difluoromethane (HFC-32), tetrafluoroethane or pentafluoroethane (HFC-125) has been used, instead of CFCs and HCFCs. For example, R410A (a pseudoazeotropic mixture of HFC-32 and HFC-125 in a mass ratio of 1:1) is a refrigerant which has been widely used. However, it is pointed out that HFCs may cause global warming.
R410A has been widely used for a common air-conditioning apparatus such as a so-called package air-conditioner or room air-conditioner, due to its high refrigerating capacity. However, it has a global warming potential (GWP) of so high as 2,088, and accordingly development of a working fluid with low GWP has been desired. Further, development of a working fluid has been desired on the condition that R410A is simply replaced and existing apparatus will be used as they are.
In recent years, a hydrofluoroolefin (HFO) i.e. a HFC having a carbon-carbon double bond is expected, which is a working fluid having less influence over the ozone layer and having less influence over global warming, since the carbon-carbon double bond is likely to be decomposed by OH radicals in the air. In this specification, a saturated HFC will be referred to as a HFC and distinguished from a HFO unless otherwise specified. Further, a HFC may be referred to as a saturated hydrofluorocarbon in some cases.
As a working fluid employing a HFO, for example, Patent Document 1 discloses a technique relating to a working fluid using trifluoroethylene (HFO-1123) which has the above properties and with which excellent cycle performance will be obtained. Further, Patent Document 2 discloses a technique relating to a working fluid using 1,2-difluoroethylene (HFO-1132) which has the above properties and with which excellent cycle performance will be obtained. Patent Documents 1 and 2 also disclose an attempt to obtain a working fluid comprising HFO-1123 or HFO-1132 and various HFCs of HFOs in combination for the purpose of increasing the flame retardancy, cycle performance, etc. of the working fluid.
However, such a HFO is a compound having an unsaturated bond in its molecule and is a compound having a very short life in the air, and accordingly under conditions under which compression and heating are repeatedly carried out in a heat cycle, it is inferior in the stability to a saturated hydrofluorocarbon or hydrochlorofluorocarbon such as a conventional HFC or HCFC, and lubricating properties may be decreased in the heat cycle system.
Thus, a method for efficiently operating a heat cycle system employing a HFO as a working fluid, with maintained lubricity while excellent cycle performance of the HFO is sufficiently made use of.